Unimolecular and collision-induced dissociation reactions of peracetylated methyl glucopyranoside

The mechanism of the collision-induced fragmentation of peracetylated methyl-α-D-glucopyranoside was investigated using deuterium-labelled acetates and sequential mass spectrometry. Loss of the substituent at C(1), the anomeric carbon, yields an ion of m/z 331, [C₁₄H₁₉O₉]⁺. This ion further dissociates via two pathways, the first including m/z 271, [C₁₂H₁₅O₇]⁺, 169, [C₈H₉O₄]⁺ and 109, [C₆H₅O₂]⁺, and the second including m/z 211, [C₁₀H₁₁O₅]⁺, 169, [C₈H₉O₄]⁺ and 127 [C₆H₇O₃]⁺. The first path proceeds via loss of acetate at C(3), followed by a single-step concerted loss of acetates from C(2) and C(4), and ending with loss of acetate from C(6). The second path proceeds predominantly via loss of acetates from C(3) and C(4), elimination of ketene from the C(2)-acetate and finally loss of ketene from the acetate at C(6). This path is also characterized by an ill-defined series of parallel decomposition reactions involving acetates from other sites on the molecule. At low collision energy, and in the absence of collision gas (unimolecular reaction conditions), the former pathway predominates; m/z 331 dissociates via loss of acetate at C(3), followed by a single-step concerted loss of acetates from C(2) and C(4).     

A convenient procedure for smooth palladium-catalyzed allylic alkylation by sodium dimethyl malonate and cyclopentadienide. A new synthesis of allylic substituted cyclopentadienes.

The use of the Pd(dba)¹₂/dpe catalytic system in allylic alkylation allows sodium dimethyl malonate to react with allylic acetates at room temperature. According to this procedure, a novel synthesis of allylic substituted cyclopentadienes is described through the use of cyclopentadienide anion as a nucleophile.     

Electron impact mass spectrometry of the acetates of zinc,magnesium, cobalt and manganese

The electron impact mass spectra of the acetates of zinc, magnesium, cobalt and manganese have been investigated using a direct inlet probe. Volatile tetrahedral complexes are produced on heating, and ions of the form [M₄(OCOCH₃)₆O]^+˙ (M = Co and Mn) and [N₄(OCOCH₃)₅O]⁺ (N = Zn or Mg) are observed. A mixture of magnesium and cobalt acetates produces ions of the form [Mg_nCo_4–n(OCOCH₃)₆O]^+˙.     

Multimerization: Association and aggregation. XIII. Concentration dependence of apparent average molecular weights of a poly-disperse associating polymer in a theta solvent

Analytical expressions are derived for the concentration dependences of different apparent average (n,w,z) molecular weights for two types (end-to-end and segment-to-segment) of open association of polymolecular unimers. The open association is defined as an association leading to an unlimited number of multimer species. The type of association depends upon the number of associogenic sites per unimer molecule: for the end-to-end type this number is constant, whereas for the segment-to-segment type it is proportional to the degree of polymerization of the unimer. For the end-to-end association, a simple relation exists between the polydispersity (M?_r)_w/(M?_r)_n of the mul-timer and the association number r and the polymolecularity (M?_I)_w/(M?_I)_n of the unimers: (M?_r)_w/(M?_r)_n = 1 + r^?1[(M?_I)_w/(M?_I)_n ? 1]. The z-average and higher averages of the r-mers may be lower than the corresponding averages of the unimers. In the theta-state, (M?_n)_app,Θ and (M?_w)_app,Θ are linear functions of c/(M?_n)_app,Θ, whereas a more complicated relation exists for the apparent higher averages. For the segment-to-segment association, both (M?_w)_app,Θ and (M?_z)_app,Θ are linear function of the weight concentration c, whereas no closed expression could be found for (M?_n)_app,Θ. For the polydispersities of multimers one finds (M?_I)_z/(M?_r)_w = 1 + r^?1[(M?_I)_z/(M?_I)_w ? 1], and, in the special case of a Schulz-Zimm distribution of unimer molecular weights, (M?_r)_n/(M?_r)_w = 1 + r^?1[(M?_I)_n/(M?_I)_w ? 1].     

Interfacial tension of liquids from the height and contact angle of a single sessile drop

The height of a sessile drop of liquid when placed on a smooth solid surface increases as the drop volume increases, until it reaches a limiting value for a very large drop. The magnitude of the height and the contact angle depends on the different physical properties of the system. A large value for the contact angle is often associated with a large value for height and vice versa. From the data of measured limiting height, Z _Θ ^∞ and contact angle,Θ, the surface or interfacial tension,γ, can be estimated using the following equation: $$\gamma = \Delta \rho \cdot g \cdot (Z_\Theta ^\infty )^2 /2(1 - \cos (\Theta ))$$ whereΔ? is the density difference between the sessile drop and that of its surrounding medium,g is the gravitational force of acceleration. In this study, the magnitude ofγ of water for various systems is estimated. These values agree with the literature values. Furthermore, the values ofγ for various liquid₁/ solid/liquid₂ systems agree with data from other methods. Thus, the above equation is valid for different liquid-solid systems. It is further shown that very accurate measurements of contact angle,Θ, can be carried out for systems in which Z _Θ Δ _? andγ are known. The variation ofΘ with the height and volume of the sessile drop is analyzed for different systems.     

Cationic polymerization of styrenes by activated covalent species. Direct 1H-NMR observation of complexes of 1-phenylethyl acetates with lewis acids

Complexes of boron trichloride, boron tribromide, and ethylaluminumdichloride with various acetates were directly observed by ¹H-NMR. Complexes of secondary and tertiary acetates which model macromolecular active species in polymerization of styrene and isobutene are stable at ?75°C, but decompose at temperatures above ?30°C to yield corresponding chlorides or bromides. The stability of complexes depends on the Lewis acid, the alkyl group in the ester, and the structure of acetate. Rates of the bimolecular exchange of complexes with excess acetate were calculated from dynamic NMR to be k_ex = 2 × 10¹ L mol^?1 s^?1 (?65°C) and k_ex = 5 × 10⁴ L mol^?1 s^?1 (?75°C) for 1-phenylethyl acetate with BCl₃ and EtAlCl₂, respectively.     

Electrical conductivity and thermopower of Fe-phosphate compounds with the lazulite-type structure

Measurements of the electrical DC and AC conductivities were performed on three Fe-phosphate compounds in the temperature range ∼210 K?T?∼450 K. The Fe-phosphates are semiconducting with activation energy of DC conductivity σ_DC of E_A∼0.35-0.45 eV. For α-Fe₂PO₄O, the AC conductivity σ_AC in the low-temperature range is considerably enhanced relative to σ_DC. The frequency dependence of σ_AC can be described by an approximate power law. For the same compound, the thermopower Θ (Seebeck effect) was found to be positive in the range ∼330 K?T?∼700 K, i.e. seemingly p-type conduction occurs; at T>700 K, Θ appears to become negative. The results are described in terms of a small polaron hopping model between localized states with electron transfer of the type Fe²⁺→Fe³⁺ with Fe²⁺ as donors. In this model Θ can be described suggesting equal concentrations of Fe²⁺ and Fe³⁺ to take part in conduction.     

Über polygermane: XI. Funktionalisierung von hexaphenyldigerman

The optimum conditions for selectively cleaving off two phenyl groups in Ge₂Ph₆ by trichloroacetic acid have been determined. Neither trihaloacetic acids nor HCl/AlCl₃ nor reactive tetrahalides MCl₄ are suitable reagents for cleaving one phenyl group alone. The ¹³C NMR chemical shifts of functional phenyl-mono- and -digermanes are given. The crystal structure of 1,2-bis(trichloroacetate)tetraphenyldigermane has been determined and refined to R = 0.048. The digermane bond is bridged by both acetates (distances GeGe 239.3(2), GeO 207.3(3) and 231.4(3) pm). The Ge atoms have trigonal bipyramidal coordination.     

Etudes par diffraction neutronique et RMN de ZnMn3C et GaMn3C0.935

Above a temperature Θ_T the perovskite type compounds ZnMn₃C and GaMn₃C_0.935 are ferromagnetic as GaMn₃C studied previously. Below Θ_T the magnetic structures of ZnMn₃C and GaMn₃C_0.935 are tetragonal noncollinear, with a ferromagnetic component along the tetragonal Oz axis and an antiferromagnetic component in the Oxy plane while GaMn₃C is a collinear antiferromagnet below Θ_T. The two compounds ZnMn₃C and GaMn₃C_0.935 show with respect to GaMn₃C the common feature of a reduction of the number of electrons, but obtained in substantially different ways, by the substitution Ga → Zn in ZnMn₃C, by the production of vacancies in GaMn₃C_0.935. By NMR we have observed resonances on ⁶⁹Ga and ⁷¹Ga which can be attributed to neighborhoods of zero, one and two C-vacancies in GaMn₃C_0.935 resonances on ⁶⁷Zn in ZnMn₃C and resonances on ⁵⁵Mn.There is a good agreement between the symmetry changes observed by neutron diffraction and NMR, between the thermal variation of the ferromagnetic components, determined by the same techniques and by magnetic measurements.     

Molecular ordering in some liquid aromatic hydrocarbons

This study presents a comparison of the structures and molecular correlations for the linear aromatic hydrocarbons: benzene, naphthalene, and anthracene in the liquid phase, performed for the first time by the method of X-ray diffraction. Also for the first time the X-ray diffraction results obtained for anthracene at 513?K have been reported. Monochromatic radiation CuK_α was used to determine the scattered radiation intensity between S _min?=?4π?sin?Θ_min/λ?=?0.417?Å^?1 and S _max?=?4π?sin?Θ_max/λ?=?7.06?Å^?1. The mean angular distributions of X-ray scattered intensity were measured and the differential radial distribution functions of electron density (DRDFs) were calculated. The mean distances between the neighbouring molecules and the mean coordination numbers were found. The most probable models of local ordering of these molecules were suggested. Correlations have been found between the number of benzene rings in the molecules studied and their physical properties.     

Yellow-green luminescence and extreme thermal quenching in the Sr6M2Al4O15:Eu2+ (M = Y,Lu, Sc) phosphor series

A series of Eu²⁺-substituted yellow-green emitting phosphors based on the compound, Sr₆M₂Al₄O₁₅ (M = Y, Lu, Sc) were identified as potential efficient phosphors based on their high calculated Debye temperatures (Θ_D > 450 K), which acts as a proxy for photoluminescent quantum yield (PLQY). The crystal structure contains corner-sharing [MO₆] octahedra and [AlO₄] tetrahedra leading to a highly connected, densely packed crystal structure. However, contrary to prediction, these compounds all showed a low PLQY (<6.5%) at room temperature. Temperature dependent luminescence measurements indicate that the photoluminescence is intense at 80 K but loses ≈90% of the emission intensity by room temperature, with the thermal quenching temperature (T₅₀) occurring well below room temperature. These results suggest that even though Debye temperature (Θ_D) is a valid proxy for PLQY, it does not describe thermal quenching.     

Ion–molecule reactions in the gas phase. XVIII.—nucleophilic substitution of diastereomeric norborneols,norbornyl acetates and benzoates under ammonia chemical ionization

The comparative behaviour of the endo- and exo-norborneols and diastereomeric derivatives (acetates and benzoates) towards the NH₃/NH₄⁺ system was investigated. It appears that the proton affinity (PA) of the substrate relative to Pa(NH₃) strongly influences competition between the protonation and nucleophilic substitution processes yielding the MH⁺ and [M + NH₄ ? H₂O]⁺ ions, respectively. Tandem mass spectrometry was used to compare collision-activated dissociation spectra of [M + NH₄ ? H₂O]⁺ with those of analogous endo- and exo-norbornylamines protonated in the source. This demonstrates that an S_Nimechanism occurs specifically for the isomeric norborneols; in contrast, for acetates and benzoates, stereospecific S_Ni and S_N2 pathways take place for exo and endo derivatives, respectively. This particular behaviour is explained by considering the steric effect induced by the endo-H at C(6). In addition, the competitive decompositions of [M + NH₄ – H₂O]⁺ into NH₄⁺ and [C₇H₁₁]⁺ daughter ions are consistent with the formation of a proton-bound complex intermediate. The observed stereochemical effects for these dauther ions are rationalized by means of arguments based on the estimated heats of formation of the transition states, which is lower for the exo-norbonyl protonated amine, consistent with anchimeric assistance, rather than a stepwise pathway which is proposed for the endoisomer.     

FT Raman spectroscopic investigation of cellulose acetate

This study reports on a new method characterizing cellulose acetates and determining the contents of acetyl groups within cellulose acetates based on FT Raman spectroscopy. Cellulose acetates exhibiting diverse degrees of substitution ascribed to acetyl groups (DS_Ac) were obtained after the deacetylation of highly acetylated cellulose, i.e. cellulose diacetate and cellulose triacetate (CTA), with aqueous sodium hydroxide solution or 1,6-hexamethylenediamine (HMDA). After plotting the Raman intensity ratios between the bands at 1,740 and 1,380 cm⁻¹ against the DS_Ac, a calibration curve with high correlation coefficient of more than 0.99 was obtained. During the deacetylation of highly acetylated cellulose, a by-product—sodium acetate (NaOAc)—forms as the most possible salt among others. In order to determine the content of NaOAc, the mixtures of cellulose acetates and NaOAc were measured with FT Raman spectroscopy. Based on the relationship between the Raman intensity ratios as I₉₂₉/I₁₃₈₀ and the contents of NaOAc in the mixtures, a calibration curve exhibiting high correlation coefficient of more than 0.99 was generated.     

New polymer syntheses 22. LC-poly(esterimide)s derived from trimellitic acid, ω-amino acids and hydroquinone or 4,4′-dihydroxybiphenyl

Diacids with variable spacer length were prepared by condensation of trimellitic anhydride and ω-amino acids. From these diacids, homopolyesters were prepared by thermal condensation with the acetates of hydroquinone or 4,4′-dihydroxy biphenyl and a series of copolyesters containing 4-hydroxy benzoic acid. The same LC poly(ester imide)s could also be prepared in a “one-pot procedure” from trimellitic anhydrid, lactams, and bisphenol acetates. The differential scanning calorimetry (DSC) traces of most poly(ester imide)s exhibit two endotherms representing the solid → LC phase transition (Tm₁) and the LC phase → isotropic melt transition (Tm₂). Observation under the polarizing microscope and wide-angle X-ray scattering (WAXS) measurements suggest that the LC phase formed immediately above the melting points (Tm₁) have a smectic character. Poly(ester imide)s of 4,4′-dihydroxybiphenyl possess higher melting points and a broader temperature range of the LC phase than those of hydroquinone. The copolyesters possess a nematic melt over a broad temperature range. Thermomechanical analyses under low pressure (0.05 kg/mm²) gave heat distortion temperatures close to the melting points (Tm₁), and under high pressure (1 kg/mm²), values between Tm₁ and the glass transition temperatures (T_g). Thermogravimetric measurements indicate that processing from the melt is feasible up to temperatures around 340°C.     

Symmetrisation of β-alkoxyalkylmercury(II) acetates

β-Alkoxyalkylmercury(II) acetates have been symmetrised in situ with alkaline sodium stannite to afford good yields of bis(β-alkoxyalkyl)mercurials, [R¹R²C(OR)CHR³]₂ Hg.     

Synthesis of fullerene C<Subscript>60</Subscript> monoadducts. Cyclopropanation of C<Subscript>60</Subscript> with sulfonium ylides

3′H-Cyclopropa[1,9](C₆₀-I_h)[5,6]fullerene-3′-carboxylic acid can be synthesized in a good yield by cyclopropanation of fullerene C₆₀ with 2-(dimethyl-λ⁴-sulfanylidene)acetates provided that the ester residue is readily hydrolyzable in acid medium.     

Spectroscopic Studies on the Interaction of Vitamin C with Bovine Serum Albumin

The mechanism of binding of vitamin C (VC) with bovine serum albumin (BSA) was investigated by spectroscopic methods under simulated physiological conditions. VC effectively quenched the intrinsic fluorescence of BSA. The binding constants K _A, and the number of binding sites, n, and corresponding thermodynamic parameters ΔG ^Θ , ΔH ^Θ and ΔS ^Θ between VC and BSA were calculated at different temperatures. The primary binding pattern between VC and BSA was interpreted as being a hydrophobic interaction. The interaction between VC and BSA occurs through static quenching and the effect of VC on the conformation of BSA was also analyzed using synchronous fluorescence spectroscopy. The average binding distance, r, between the donor (BSA) and acceptor (VC) was determined based on Förster’s theory and was found to be 3.65 nm. The effects of common ions on the binding constant of VC-BSA were also examined.     

Reactions d'alkylation de chlorures,formate et acetates allyliques catalyses par des complexes du fer et du cobalt

Alkylation of allylic substrates (chlorides, acetates, formate) with diethyl malonate anion is catalysed by the iron complexes (η³-crotyl) Fe(CO)₂NO (chlorides only) and Fe(CO) ₃NO^?Na⁺ with good regioselectivity. (η³-crotyl) Co(CO)₃ and Co(CO)₄^?Na⁺ are also active catalysts.     

Osmotic coefficient data for NaOH–NaCl–NaAl(OH)4–H2O system measured by an isopiestic method and modeled using Pitzer's model at 298.15 K

Osmotic coefficient data were obtained for the aqueous solutions of NaOH–NaCl–NaAl(OH)₄. The solutions were prepared by dissolving AlCl₃·6H₂O in aqueous NaOH solutions. The osmotic coefficients of the solutions were measured by an isopiestic method at 25°C. The osmotic coefficient data were used to evaluate the unknown binary and mixing parameters of Pitzer's model for the aqueous NaOH–NaCl–NaAl(OH)₄–H₂O system. The binary Pitzer's parameters, β⁽⁰⁾, β⁽¹⁾, and C^φ, for NaAl(OH)₄ were found to be −0.0083, 0.0710, and 0.00184 respectively. These binary parameters were obtained from the data on the ternary system. This was necessary since it was not possible to prepare a single (NaAl(OH)₄) solution. The mixing parameters, Θ_{OH⁻Al(OH)⁻4}, Θ_{Cl⁻Al(OH)⁻4}, Ψ_{Na⁺OH⁻Al(OH)⁻4}, and Ψ_{Na⁺Cl⁻Al(OH)⁻4} were found to be −0.2255, −0.2430, −0.0388, and 0.2377 respectively. The experimental osmotic coefficient data were correlated well with Pitzer's model using the parameters obtained.